Perpendicular magnetic recording (PMR) has been developed in part to achieve higher recording density than is realized with longitudinal magnetic recording (LMR) devices and is believed to be the successor of LMR for next generation magnetic data storage products and beyond. The advantages of PMR associated with a soft underlayer (SUL) from PMR media can reduce both sensor track width (MRW) and magnetic write width (MWW) significantly. A single pole writer combined with a soft magnetic underlayer also has the intrinsic advantage of delivering higher write field than LMR heads. However, side fringing from a trailing shield PMR head is substantially larger than in LMR. The large side fringing for PMR heads is a primary concern for the push to higher track density (TPI) and is a major constraint to PMR extendability.
A conventional PMR write head as depicted in FIG. 1 typically has a main (write) pole 10 with a small surface area (pole tip) at an air bearing surface (ABS) 5 and a flux return pole (opposing pole) 8 which is magnetically coupled to the write pole through a trailing shield 7 and has a large surface area at the ABS. Magnetic flux in the write pole layer 10 is generated by coils 6 and passes through the pole tip into a magnetic recording media 4 and then back to the write head by entering the flux return pole 8. The write pole concentrates magnetic flux so that the magnetic field at the write pole tip at the ABS is high enough to switch magnetizations in the recording media 4. A trailing shield (not shown) is added to improve the field gradient in the down-track direction.
In FIG. 2, a top view is shown of a typical write pole layer 10 otherwise known as the main pole layer or main write pole. The write pole 10 has a narrow section 10n that extends a neck height (NH) distance from the ABS plane 5-5 to a plane 3-3 parallel to the ABS where a middle section 10m having sides 10s flares out at an angle θ from a dashed line 11 that is an extension of one of the sides of narrow section 10n. There is also a third main write pole section 10r that has one end at the plane 9-9 where the flared sides 10s terminate and extends a certain distance away from the plane 9-9 in a direction perpendicular to the ABS.
To achieve high areal recording density with PMR technology, key requirements for the PMR writer design are to provide large field magnitude and high field gradient in both down-track and cross-track directions. In practice, these two requirements are often traded off with each other to balance the overall performance. There are two approaches to achieve these requirements. One approach involves optimizing the geometry of the main write pole such as modifying the values for NH and flare angle θ. A short NH or large θ can increase write field magnitude effectively. However, too short of a NH leads to problems of meeting process tolerance during manufacturing while too large of a flare angle θ may cause a large amount of adjacent track erasure (ATE) because of a large fringe field. In today's commercial PMR writer products, NH is generally above 0.1 micron and flare angle θ is kept less than 45 degrees. A second design approach involves applying magnetic shield structure in the vicinity of the main write pole as described by M. Mallary in “One Terabit per Square Inch Perpendicular Recording Conceptual Design”, IEEE, Trans. Magn., Vol. 38, July, 2002. To further improve cross-track field gradient, a full side shield writer structure is used to limit the excessive fringe field onto the adjacent track. Depending on the spacing between the side shield and the write pole, field magnitude could drop below the minimal performance requirement. As a result, flux intensity will be reduced at the ABS and writability will decrease.
As recording density keeps increasing, the trade-off between writability and field gradient becomes more challenging. Therefore, all the design elements must be integrated and optimized simultaneously to achieve best performance. Unfortunately, none of the prior art structures provide satisfactory control of field magnitude and field gradient in both the down-track and cross-track directions. Therefore, an improved write structure is necessary to achieve the high performance required for advanced devices with narrow track widths and high recording density.
A search of the prior art revealed the following references. U.S. Patent Application 2007/0253107 shows that a trailing shield and side shield may be a single piece. A non-conformal side gap is depicted where the side gap length between a side shield and pole tip section narrows with increasing distance from the ABS.
In U.S. Patent Application 2008/0100959, a conformal side gap is illustrated where the side gap is larger than the write gap.